lfs-book/chapter06/readjusting.xml

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<sect1 id="ch-system-readjusting">
  <?dbhtml filename="readjusting.html"?>

  <title>Re-adjusting the Toolchain</title>

  <para>Now that the final C libraries have been installed, it is time to adjust
  the toolchain again. The toolchain will be adjusted so that it will link any
  newly compiled program against these new libraries. This is a similar process
  used in the <quote>Adjusting</quote> phase in the beginning of <xref
  linkend="chapter-temporary-tools"/>, but with the adjustments reversed. In <xref
  linkend="chapter-temporary-tools"/>, the chain was guided from the host's
  <filename class="directory">/{,usr/}lib</filename> directories to the new
  <filename class="directory">/tools/lib</filename> directory. Now, the chain will
  be guided from that same <filename class="directory">/tools/lib</filename>
  directory to the LFS <filename class="directory">/{,usr/}lib</filename>
  directories.</para>

  <para>First, backup the <filename class="directory">/tools</filename> linker,
  and replace it with the adjusted linker we made in chapter 5. We'll also create
  a link to its counterpart in <filename class="directory">/tools/$(gcc
  -dumpmachine)/bin</filename>.</para>

<screen><userinput>mv -v /tools/bin/{ld,ld-old}
mv -v /tools/$(gcc -dumpmachine)/bin/{ld,ld-old}
mv -v /tools/bin/{ld-new,ld}
ln -sv /tools/bin/ld /tools/$(gcc -dumpmachine)/bin/ld</userinput></screen>

  <para>Next, amend the GCC specs file so that it points to the new
  dynamic linker, and so that GCC knows where to find its start files.
  A <command>perl</command> command accomplishes this:</para>

<screen><userinput>gcc -dumpspecs | \
perl -p -e 's@/tools/lib/ld-linux.so.2@/lib/ld-linux.so.2@g;' \
    -e 's@\*startfile_prefix_spec:\n@$_/usr/lib/ @g;' &gt; \
    `dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>

  <para>It is a good idea to visually inspect the specs file to verify the
  intended change was actually made.</para>

  <important>
    <para>If working on a platform where the name of the dynamic linker is
    something other than <filename class="libraryfile">ld-linux.so.2</filename>,
    substitute <quote>ld-linux.so.2</quote> with the name of the platform's
    dynamic linker in the above commands. Refer back to <xref
    linkend="ch-tools-toolchaintechnotes" role=","/> if necessary.</para>
  </important>

  <caution>
    <para>It is imperative at this point to stop and ensure that the basic
    functions (compiling and linking) of the adjusted toolchain are working
    as expected. To do this, perform a sanity check:</para>

<screen><userinput>echo 'main(){}' &gt; dummy.c
cc dummy.c -Wl,--verbose &amp;&gt; dummy.log
readelf -l a.out | grep ': /lib'</userinput></screen>

    <para>If everything is working correctly, there should be no errors,
    and the output of the last command will be (allowing for
    platform-specific differences in dynamic linker name):</para>

<screen><computeroutput>[Requesting program interpreter: /lib/ld-linux.so.2]</computeroutput></screen>

    <para>Note that <filename class="directory">/lib</filename> is now
    the prefix of our dynamic linker.</para>

    <para>Now make sure that we're setup to use the correct start files:</para>

<screen><userinput>grep "/usr/lib/crt.* " dummy.log</userinput></screen>

    <para>If everything is working correctly, there should be no errors,
    and the output of the last command will be:</para>

<screen><computeroutput>attempt to open /usr/lib/crt1.o succeeded
attempt to open /usr/lib/crti.o succeeded
attempt to open /usr/lib/crtn.o succeeded</computeroutput></screen>

    <para>Next make sure that we're using the correct libc:</para>

<screen><userinput>grep "/lib/libc.so.6 " dummy.log</userinput></screen>

    <para>If everything is working correctly, there should be no errors,
    and the output of the last command will be:</para>

<screen><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>

    <para>Lastly, make sure GCC is using the correct dynamic linker:</para>

<screen><userinput>grep found dummy.log</userinput></screen>

    <para>If everything is working correctly, there should be no errors,
    and the output of the last command will be (allowing for
    platform-specific differences in dynamic linker name):</para>

<screen><computeroutput>found ld-linux.so.2 at /lib/ld-linux.so.2</computeroutput></screen>

    <para>If the output does not appear as shown above or is not received
    at all, then something is seriously wrong. Investigate and retrace the
    steps to find out where the problem is and correct it. The most likely
    reason is that something went wrong with the specs file amendment
    above. Any issues will need to be resolved before continuing on with
    the process.</para>

    <para>Once everything is working correctly, clean up the test
    files:</para>

<screen><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>
  </caution>

</sect1>